When city or county firefighters have a family event or unexpected obligation pop up on a workday, their solution is familiar to most shift workers: They find a colleague willing to trade hours.

But for the roughly 10,000 firefighters employed by the federal government at places such as the Naval Academy and Fort Meade, law limits the ability to swap shifts — a restriction that they say causes them to miss birthdays, graduations and personal emergencies.

And so the small federal firefighting force — including about 350 in the Baltimore-Washington region — is again pushing Congress to grant them the same flexibility to alter schedules that their local counterparts have had for decades under the Fair Labor Standards Act.

"There are things you miss, like when your child has a play, or some sort of activity," said Trenton Massenberg, 47, a fire captain at the Walter Reed National Military Medical Center in Bethesda. "We do the same job as the municipal fire department, and the municipal fire departments are allowed to do this."

Despite bipartisan support and virtually no public opposition, efforts to change the law have failed for years. But proponents believe the political pieces might now be in place to advance legislation drafted by Rep. John Sarbanes to change the rules.

The shift-swapping issue, known as trade time, is one of several battles that unions representing the firefighters are waging with federal agencies. The force has long sought to change the way retirement contributions are calculated to include overtime that many federal firefighters are required to work. That effort is under way again this year.

Addressing another concern, President Barack Obama directed the Office of Personnel Management to grant health insurance to seasonal federal firefighters after meeting with several of them in Colorado last year.

Most of the issues related to trade time stem from an unusual schedule — 24 hours on, 24 hours off — that is common for firefighters but doesn't fit neatly with the federal government's more traditional office hours. Federal firefighters employed by the Defense Department can regularly work as much as 19 hours of mandatory overtime each week.

Not only does that schedule complicate payroll, the 24-hour shifts leave little room to squeeze family responsibilities into workdays. Firefighters are allowed to swap hours within a two-week pay period, but they say it is virtually impossible to do so in the last days of a pay cycle.

"Federal firefighters are out there putting themselves on the line every day," said Sarbanes, a Maryland Democrat whose district includes the Naval Academy. "This kind of flexibility is the least we can do."

The House approved the legislation on a voice vote that year, but it died in the Senate over procedural objections.

Supporters say Oklahoma Sen. Tom Coburn raised those objections. They said they hope the process will go more smoothly this year because Coburn now serves as the ranking Republican on the Homeland Security and Government Affairs Committee — giving him greater control over how the bill advances.

A Coburn spokesman did not respond to questions.

Greg Russell, president of the National Capital Federal Fire Fighters, said he believes the Defense Department has also quietly worked against the measure, citing concerns about record-keeping and resolving disputes — making a "mountain out of a molehill," in his words.

But the Pentagon has never publicly opposed the bill. A spokesman, Mark Wright, said the Defense Department does not comment on pending legislation.

The across-the-board federal budget cuts known as sequestration might also give the measure a push this year. The cuts will result in furloughs at federal fire stations, further complicating schedules.

Supporters say the measure would save money, though no independent analysis has been performed to back up that claim. If firefighters must take time off unexpectedly and can't find trade time within the pay period, they might be tempted to call in sick — though that is prohibited — requiring supervisors to offer overtime to others to cover the shift.

Russell said the measure shouldn't cost taxpayers anything, and he rejected the idea that swaps would create a headache for supervisors.

Russell's union, part of the International Association of Fire Fighters, represents firefighters at the Naval Academy, Naval Air Station Patuxent River and several other military facilities in Maryland, Virginia and the District of Columbia.

"It's a gentleman's agreement," he said. "All this amounts to is Smith and Jones changing their names on a duty roster."